The present invention relates to an apparatus and method for insuring a flat hem portion in a moving film-like web in a hem forming machine.
In forming a draw tape bag, a plastic web is supplied from a roll of indefinite length in a continuous flow to form a series of like bags. U.S. Pat. No. 4,624,654 which issued Nov. 25, 1986 and U.S. Pat. No. 4,664,649 which issued May 12, 1987 disclose draw tape bag forming apparatus for forming a plastic bag with a draw-tape for closing the bag from a prefolded continuously moving web, with special means for folding the edges to form aligned hems which are heat sealed. A method and apparatus for forming a draw tape bag from a flat sheet-like web is shown the in copending application of Robert J. Wech entitled "Draw Tape Bag Forming Method and Apparatus", which was filled on even date herewith and is assigned to a common assignee herewith. Generally, as disclosed therein, a roll of a pliable plastic sheet web is mounted in an unwind stand. The plastic sheet is withdrawn and passed through a series of stations for forming a series of draw tape bags. Generally, the flat web is fed into a hem former which is adapted to fold the edges of the web inwardly to form a hem portion which receives a draw tape through a tape inserter unit followed by heat sealing of the hem. The hemmed plastic sheet is folded on itself, and passed through a bag making machine or apparatus which transversely seals and severs the folded web on longitudinally spaced transverse areas to complete the series of the draw tape bags.
In operation of draw tape bag apparatus, inferior bags may be encountered if the hems are not flat. As the hemmed and holded web moves through the hem forming apparatus, the hem walls may tend to separate from the desired flat condition for optimum machine operation.
There is therefore a need for a method and apparatus to positively insure a flat, folded web for final on-line movement through the bag making apparatus.